Check valves are routinely used to permit fluid flow in but one direction, with two common types thereof being the ball check valve and the poppet valve. Both types may include a spring to bias the sealing member, either the ball or the poppet, against the valve seat to maintain a seal until the upstream fluid pressure, acting against the sealing member, exceeds the spring force to unseat the sealing member to allow fluid flow above a predetermined fluid or crack pressure.
Elastomeric material seats are commonly used in both of the noted types of check valves, as this material provides for an excellent and reliable seal at both low and high fluid pressures. Since elastomeric materials are resilient, the nature of elastomeric seals is dynamic, which only requires a minimum force to bias the ball or poppet against the valve seat to produce a seal at either low or high fluid operating pressures. Many check valve designs limit the bias force of the ball or poppet against the seat since excessive force can damage the elastomeric material and cause the valves to leak. However, elastomeric seals are limited in application, typically by either degradation, caused by chemical attack, or extreme low or high operating temperatures.
Thermoplastic materials are often used as replacements for elastomeric materials when these noted conditions apply. However, thermoplastic materials, unlike elastomeric materials, are not resilient and therefore are not well suited to provide for reliable dynamic seals. Thermoplastic materials provide the most effective seals under static loading conditions, requiring compressive forces that must increase with increasing fluid pressures to maintain their seals. However, thermoplastic materials also have high coefficients of thermal expansion and low compressive yield strengths that decrease rapidly with increasing operating temperatures. They also deform permanently, over time, at stress levels well below their yield strengths, and deform in greatly increasing amounts at higher operating temperatures, all of which can create difficulties when thermoplastic materials are used for seat materials in check valves.
In the existing art, some check valve designs offer thermoplastic seats as an option for elastomeric material seats, with either identical or closely similar valve seat geometries. However, check valves designed for resilient dynamic seals will not perform well with non-resilient seat materials. This is reflected in published limitations on seal tightness as well as temperature and pressure limits which fall well below the full capabilities of thermoplastic materials.
Other types of valve designs that commonly use thermoplastic materials for valve seats, such as quarter turn ball valves, offer seal tightness performance at pressure and temperature operating ranges that typically exceed those for existing check valves. It is therefore desirable and possible to improve upon the design of existing art ball check valves with thermoplastic seat materials such that a ball check valve will provide an equal or superior level of seal performance to that of a quarter turn ball valve.
The design and construction of the present invention is focused on easily replaceable, generally soft and somewhat flexible non-resilient plastic material, such, as for example, fluoroplastic material, valve seats. Such seats are machined or molded to final shape and separate coining is not required. These seats do have arcuate/spheric seating surfaces, but the seat radii thereof are slightly larger, by design, than the radii of the mating balls, thus permitting self-compensation for pressure and temperature. In addition, the amount of seat seal area can be designed specifically for a particular seat material, based on its mechanical properties and desired temperature and pressure operating conditions, all of which will be explained in more detail hereinafter.
The patent literature includes a large number of ball check valve constructions, with FIG. 4 of U.S. Pat. No. 5,107,890, to Gute, which pertains to a ball check valve, showing a curved seating surface matched to the ball. However, it is stated therein that the coined arcuate (curved) seating surface is complimentary to the ball surface to reduce leakage and the claimed method of manufacturing the seat requires a coining operation to “form a desired arcuate configuration seating surface”. In addition, the seat is generally manufactured from a brass material and that the seat is press-fit or friction fit into the valve body. As previously noted, the seat of the present invention is formed of a non-resilient plastic material and has an arcuate/spherical seating surface having a radius slightly larger than the radius of the ball, thus permitting self-compensation for pressure and temperature.
U.S. Pat. No. 4,197,875, to Schieferstein et al., and U.S. Pat. No. 5,749,394, to Boehmer et al., both pertaining to check valves, set forth that the seats are constructed of elastomeric sealing material, not the thermoplastic seat material of the present invention, and these constructions also use a conical seat which is a of a completely different geometry than the spherical design and construction of the seat of the present invention. Further prior art patents, relating to ball check valves additionally include: U.S. Pat. No. 3,040,771 to Droitcour et al.; U.S. Pat. No. 4,084,304 to Myers; U.S. Pat. No. 4,541,412 to Bagshaw et al.; U.S. Pat. No. 4,613,738 to Saville; U.S. Pat. No. 4,736,083 to Saville; U.S. Pat. No. 5,251,664 to Arvidsson et al.; and U.S. Pat. No. 6,250,336 B1 to Murphy et al. However, none of these prior art structures disclose a spherical ball valve received within a spherical seat seal, where the seat seal is preferably formed of a fluoroplastic-type material and has a radius slightly larger than the radius of the mating ball.